Ovarian cancer is the fourth leading cause of cancer-related death among women. The relatively poor prognosis for ovarian cancer reflects the high incidence of metastasis at diagnosis. Indeed, 75% of patients are diagnosed with metastatic disease, which has a 5-year survival of 20-25%. The high mortality rate is due in large part to the lack of effective treatment options for metastatic cancer. Identifying the mechanisms that regulate ovarian cancer metastasis will provide much needed additional therapeutic targets for the treatment of ovarian cancer. We hypothesize that the integrin mediated interaction between the tumor cells and mesothelium is an important component of ovarian cancer progression. Ovarian carcinomas metastasize by invading through the mesothelium, a layer of mesothelial cells that line the peritoneal cavity. We reported a novel mechanism for the regulation of mesothelial invasion. Our data demonstrate that VCAM-1, which is expressed preferentially on the mesothelium of ovarian cancer patients, functions together with its ligand, a41 integrin (expressed on ovarian cancer cells), to promote mesothelial invasion in cell culture systems. Importantly, inhibition of VCAM-1 function increased survival and decreased tumor burden in a mouse model of ovarian cancer peritoneal metastasis. Our preliminary data demonstrate that lysophosphatidic acid (LPA), a bioactive phospholipid found in abundance in the peritoneal cavity of ovarian cancer patients, regulates mesothelial invasion and mesothelial VCAM-1 expression. Importantly, chronic production of LPA by mesothelial cells results in constitutive VCAM-1 expression that is refractory to other stimuli, including TNF-a, a well- characterized regulator of VCAM-1 expression. The goal of this proposal is to determine the mechanisms that regulate VCAM-1 expression on the mesothelium of ovarian cancer patients. This will be accomplished with the following specific aims: 1) determine the signaling pathways initiated by LPA and TNF-a that regulate VCAM-1 expression in mesothelial cells; 2) define the contribution of macrophages and mesothelial cells to VCAM-1 expression and ovarian cancer progression; and 3) identify the clinical parameters that correlate with mesothelial VCAM-1 expression in ovarian cancer patients. Understanding the factors that regulate VCAM-1 expression in ovarian cancer patients will provide insights into the design of new opportunities for therapeutic intervention. Successful completion of these aims is expected to provide important mechanistic information about mesothelial cells, which play a critical role in ovarian cancer peritoneal metastasis. Additionally, understanding the mechanisms by which LPA promotes VCAM-1 expression has implications for the treatment of other diseases characterized by chronic VCAM-1 expression, including autoimmunity and atherosclerosis.